Based on some experimental "hacking" I did last week in Newcastle, I
think the libsbml bindings currently only work for Python version 2.3
(which comes bundled with Mac OSX), not more recent versions (2.4 and 2.5).
I can provide more details if required...
This is not an urgent bug (I can revert to an older version of python),
but it would be nice to have it sorted in the future.